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[Groff] Re: grohtml and diversions

From: Werner LEMBERG
Subject: [Groff] Re: grohtml and diversions
Date: Fri, 11 Apr 2003 23:49:32 +0200 (CEST)

> I've been drinking plenty of black coffee and thinking hard about
> these issues..  I wonder whether a different tack might be taken.
> What about defining a new class, say `tag' which can be chained to
> other tags and the head of this tag list can be stored on a glyph
> node, or on diversion node.

I think it is better to maintain two `state tables' instead: One which
covers the troff state (e.g. line length, indentation, etc. --
approximately a small subset of the `environment' class) and another
which covers the html state, i.e., the html tags emitted in the troff
intermediate output to guide post-grohtml.  With your approach, e.g.

  .ll 5i
  .ll 3i
  .ll 2i

produces three tags attached to `a' which is not efficient (if you
want to avoid that you have to maintain a state table even with your

> When one of
> >   .br
> >   .ce
> >   .fi
> >   .fl
> >   .in
> >   .ll
> >   .nf
> >   .po
> >   .ps
> >   .rj
> >   .sp
> >   .ta
> >   .ti
> is seen a tag is created and appended to the current list of
> outstanding tags.  When a glyph is created then the current list of
> outstanding tags is placed into the glyph.  As tags are placed onto
> glyphs they cannot have any white space surrounding them.  A tag may
> be created in a complete state (the value is known) or an incomplete
> state in which case the value must be discover just before they are
> written to post-grohtml.

Hmm, I think this won't work.  As far as I can see, there is no
`incomplete state' within troff.

> In your first example we have:
>   .di xxx
>   .ll 5i     <tag .ll 5i complete> and put on outstanding list
>   a          outstanding list is placed onto glyph a's list.
>              outstanding list is reset.

My approach: As soon as the first glyph is emitted to the diversion
(`a' in the example), output the *complete troff state* (this is
something new which I haven't suggested in the previous mail).  This
is, we have a series of

  \!\X'html-tag: .ll ...'
  \!\X'html-tag: .in ...'

(the \! is used because we are in a diversion).  Perhaps we shall add
a special single tag to do that efficiently.

Partial emission won't work (this I have found out today).  Consider

  .ll 5i
  .di xxx
  .ll 3i

While emitting `xxx' we have to know that the line length was 5i
as `xxx' has been defined.

>   .br        <tag .br complete> and added to outstanding list

My approach: Emit \!\X'html-tag: .br'.

>   .ll        <tag .ll incomplete> and appended to outstanding list

Nothing with my approach.  This `.ll' does *not* belong to the
diversion at all!  It only changes the troff state, thus it shouldn't
be recorded in the diversion.

>   .di        outstanding list placed onto diversion, xxx, tag list.
>              outstanding list is reset.

Nothing with my approach.

>   x\*[xxx]   glyph x is emitted and the diversion xxx is processed.

My approach: Before emitting glyph `x' check whether the troff state
has changed and emit tags if necessary.  Before emitting `xxx' save
the html state on a stack.

>              <tag .ll 5i is emitted> (was found on `a' list)

My approach does nothing special here; now the \!\X'...' stuff already
part of the diversion simply gets expanded.

>              glyph a is emitted

Again, with my approach the troff state has to be checked and tags
emitted if necessary.

>              now the tags found on diversion xxx are emitted
>              <tag .br> emitted

Nothing special with my approach.

>              <tag .ll incompete> is discovered, therefore evaluate
>                                  this and emit tag.

This is wrong IMHO as explained above.

After ending the diversion, the html state must be restored (emitting
tags if necessary) and popped off the stack.


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